<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            /* 清除内外边距 */
            margin: 0;
            padding: 0;
        }

        div {
            height: 3000px;
            /*图片固定在页面*/
            background-attachment: fixed;
            /*将图片放在盒子的中间*/
            background-position: center;
            /*将图片最大化在盒子中*/
            background-size: cover; 
        }

        .z {
            background-image: url(../img/one.jpg);
        }

        .x {
            background-image: url(../img/two.jpg);
        }

        .c {
            background-image: url(../img/shree.jpg);
        }
    </style>
</head>

<body>
    <div class="z"></div>
    <div class="x"></div>
    <div class="c"></div>
</body>
</html>